In recent years, attention has been given to display devices in which a touch detection device referred to as a so-called touch panel is provided on a display device such as a liquid crystal display device, or a touch panel and a display device are integrated as a single body, and the display device is made to display various button images to enable information to be input without ordinary real buttons. Such display devices having a touch detection function do not need input devices such as a keyboard, a mouse and a keypad, and thus tend to be broadly used as display devices of computers, portable information terminals such as cell phones, etc.
As such a touch panel, a capacitive touch panel is known in which a plurality of electrodes each formed to extend in a single direction are intersected to each other. In this touch panel, the electrodes are connected to a control circuit, and when supplied with an excitation current from the control circuit, they detect an object close thereto.
As a display device provided with a touch sensor, a so-called in-cell touch panel is proposed in addition to a so-called on-cell touch panel in which a touch panel is provided on a display surface of a display device. In the in-cell display device, a common electrode for display, which is originally provided in the display device, is also used as one of a pair of electrodes for a touch sensor, and the other of the pair of electrodes (a touch detection electrode) is provided to intersect the common electrode.
Furthermore, as methods of detecting a touch position, a mutual detection method and a self-detection method are known. In the mutual detection method, a drive signal of alternating voltage is input to one of electrodes, and a detection signal generated in the other electrode by the drive signal is processed, to thereby detect a touch position. In the self-detection method, drive signals of alternating voltage are input to electrodes, respectively, and signals generated in the electrodes, respectively, are processed, to thereby detect a touch position.
Incidentally, in a display device provided with an in-cell touch sensor, if a common electrode for display which is provided in the display device is used as an electrode for the touch sensor, there is a possibility of a display being influenced by a parasitic capacitance generated between the common electrode and drive lines (source lines, gate lines, etc.). In recent years, the influence of the parasitic capacitance has been grown since display panels have been made to have a larger size and also a higher resolution. This can cause their display functions to be remarkably worsened.